The broad objective of this proposal is to understand how chromatin structure affects the distribution of carcinogen damage to DNA and its repair in human cells. Recent advances in the understanding of chromatin structure along with the methodology developed in this laboratory to analyze DNA damage and DNA repair synthesis make possible a comprehensive study of the distribution, within chromatin, of DNA damage by chemical carcinogens (e.g., N-acetoxy-2-acetylaminofluorene (NA-AAF) and a physical carcinogen (UV radiation). DNA damage and repair within the different structural regions of chromatin will be measured by analysis of the kinetics of digestion with staphylococcal nuclease and DNAase I. Recent observations indicate that UV-induced pyrimidine dimers are removed much more rapidly than are covalently bound adducts of NA-AAF. Hence, the initial phase of this study will concentrate on determining whether or not this difference is the result of differences in the distribution of damage to DNA within chromatin by a chemical and a physical carcinogen and/or differences in the repairability of the different regions of chromatin. The second phase involves a comparison of the distribution of damage and repair of NA-AAF and UV radiation in the chromatin of normal human cells and repair difficient human (xeroderma pigmentosum) and mouse cells. Once the methodology and basic concepts are worked out for these two well characterized carcinogens, the chromatin distribution patterns for the enrironmentally relevant carcinogens 7,8-dihydro-9,10-epoxybenz(a)pyrene, 7-bromomethylbenz(a)anthracene, and methylnitrosourea will be determined.